Unsymmetrical dialkyl hydroquinone



United States Patent UNSYMMETRICAL ,DIALKYL HYDROQUINONE ANTISTAIN AGENTS John R. Thirtle, Paul W. Vittumyanil Arnold Weissberger,

Rochester, ,N. Y., assignorsno .Eastman Kodak Company, Rochester, N. Y., a corporationofNew Jersey N Drawing. Application June '3, 1953, Serial No. 359,442

4 Claims. (Cl. 95-6) This invention relates to color photography and ,particularly to a method for preventing the formation of color fog or stain in photographic emulsions.

The method .of .color photography in which colorforming or coupler compounds combine with the development product of aromatic amino photographic developers to produce dyes is wellknown. The color formers or couplers may be added directly -to the emulsion layers or may be incorporated in the developing solution as described in Fischer U. S. Patent 1,102,028, granted June 30, 1914, or they may be incorporated in a water-permeable medium which is insoluble in the carrier for the sensitive silver salt as described in Marines and Godowsky U. S. Patent 2,304,940, December 15, 1942, and Jelley and Vittum U. S. Patent 2,322,027, granted June 15, 1943.

A difiiculty frequently encountered in these processes is the formation of color fog "or stain. This stain, which appears in the highlight orwliite .areas of processed pictures, may originate from several diiferent causes. One cause may be that a small amount of developing agent is oxidized by the oxygen of theair, producing oxidized developer in small amounts which reacts with the colorforming couplers throughout thewhollepicture area. As a result, inthe highlight areas 0f the picture 'in'whic'h no exposure of the silver halide has "occurred, some dye stain is formed. An appreciable part of "the dye stain may result from silver fog. It is well known that color development produces a marked intensification 'eifect, that is, that an amount of silver whichis barely discernible will be associated with a fairly high dye :density. Accordingly, a very small amount of silver fog 'in a color-developed image will be accompanied by an appreciable dye fog or stain. This small amount .ofsilver fog is usually not readily controlled by the same procedures used to reduce higher amounts of silver fog to the level which is acceptable in black-and-white development.

The control of color fog or tstain byjncorporatingih? droquinone or certain of its-derivatives in photographic emulsions is described in Vittum and Wilder U. :SnPatent 2,360,290, granted October 10, 1944. Hydroquinones described therein include diamyl hydroquinone and dioctyl hydroquinone. The dialkyl hydroquinones available at that time were the di-secondary and di-tertiary hydroquinones such as 2,5-di-tertiary octyl hydroguino'ne. This compound has good stain preventing propertieswhen incorporated in photographic color films but it suffers from .strong enough reducing agents .to .react rapidly with oxi- .dized color developer. A further object is to provide antistain agents which do not form highly colored oxidation products when the material containing them is put through an oxidizing hath. Other objects will appear from the following description of our invention.

'These objects are accomplished 'by the use in an emulsion layer or other layer of a photographic material especially a silver halide emulsion layer in which a colored image is formed by development in a color-forming developer, of an unsymmetrical 2,5- or 2,6-dialkyl hydroquinone'having the formula in which R represents an-alkyl group of from .2 to 18 carbon atoms e. g., ethyl, propyl, n-hexadecyl, secondary octadecyl, etc., and R represents an alkyl group tOf :from 1 to 18 carbon atoms, R being a different alkyl group than R and being attached to 'the-hydroquinone in the 5 or 6 position.

.The 1following examples illustrate the compounds usean according to our invention:

the disadvantage when used in silver halide emulsion yellow paste under the aqueous layer.

in Z-n-hexadecy1-6 niethyl-lfidroquinone The compounds illustrated above are prepared as fol- 'lows:

Compound 1.-2-methyl-S-palmitoylhydr0quinone A one-liter, v3-necked flask .-equiped .with a stirrer, a gas inlet tube reaching near the bottom of the flask, and a gas outlet tube to the hood, was charged with a mixture of 62 g. (0.5 mole) of toluhydroquinorre, 192 g. (0.75 mole) of'palmitic acid, and 325 cc. of s-tetrachloroethane. Boron trifiuoride was introduced with stirring for five hours; little heat was evolved and a'near solution-resulted. After standing overnight,the reaction mixture was treated with more boron trifluoride for one'hour while stirring and heating on a steam bath, .then heated with stirring for eighthourslonger.

The reaction mixture .was allowed to stand overnight and was then poured into a solution .of 205 .g. of sodium acetate in 2 liters of water. Mechanicalstirring gave a The latter was decanted and the paste stirred with 1250 cc. petroleum ether until a thick slurry resulted (ca. 15 min). The solid was collected on an 18.5 cm. Biichner funnel and washed with 500 cc. more petroleum ether, followed by 2 liters of water. The material, dried in a steam cabinet at 40 C., weighed 137 g. (75.7%) and contained some inorganic material. Recrystallization from 2400 cc. of ethyl alcohol diluted with 600 cc. of water gave pale yellow needles which were collected and washed with a mixture of 400 cc. of alcohol and 100 cc. of water. The yield was 124 g. (68.5%), M. P. 94-94.5 C. with a little softening at 91 C.

Z-n-h exadecyl- -meth ylh yd roquinone A mixture of 7.25 g. (0.02 mole) of Z-methyl-S-palrnitolylhydroquinone, 0.8 g. of palladium on charcoal catalyst, and 100 cc. of glacial acetic acid was shaken under hydrogen at 25 p. s. i. for 4 hours at 25 C. The product had formed a thick slurry. The mixture of product and catalyst, collected on a Biichner funnel, was reheated with 100 cc. of glacial acetic acid and filtered. The pale yellow filtrate deposited 6.2 g. (90%) of pale pink crystals, M. P. 127-1285 C., on standing overnight. Treatment with a little zinc dust in 100 cc. of glacial acetic acid and filtration gave on cooling 5.7 g. (82.7%) of pure white needles, M. P. l27128 C.

Compound 2.--2-sec. octadecyl-5-methylhydr0quin0ne A mixture of 62 g. (0.5 mole) of toluhydroquinone, 126 g. (0.5 mole) of l-octadecene, and 68 g. (0.5 mole) of anhydrous zinc chloride was stirred vigorously and heated at 200-210 C. for 3 hours. The stirring was stopped and the reaction mixture allowed to cool to 100 C. The fluid was decanted from the tar, diluted with 150 cc. of benzene, and extracted twice with 100-cc. portions of 10% hydrochloric acid, followed by two 200-cc. portions of hot water. A further 250 cc. of hot benzene was added and the hot solution extracted with hot water until no longer acid to Congo red. The benzene layer was dried superficially with sodium sulfate, concentrated, and distilled, giving 82 g., b0.5, 200-225 C. Redistillation gave 65 g. (34.5%), box), 210 C.

Compound 3.4 methoxy 2 methyl 6 palmitoylphenol A solution of 17 g. (0.12 mole) of 4-methoxy-2-methylphenol (Beilstein, 6, 874, Supp. 429) and 46.1 g. (0.18 mole) of palmitic acid in 450 cc. of dry tetrachloroethane was kept saturated with boron trifluoride gas for 5 hours. The reaction mixture was heated on a steam bath for 5 hours, then stirred into sodium acetate solution (ca. 5 g. in 500 cc. H2O). Enough ether was added to cause the organic solution to float. The aqueous layer was extracted with more ether and the solutions were combined, dried, and concentrated. Fractional distillation gave 24.3 g. (52.5%), b1 205-215"; M. P. 59-62". Recrystallization from 290 cc. of 95% ethyl alcohol gave 17.1 g., M. P. 66-67 6-hexadecyl-4-methoxy-Z-methylphenol Two 8.3 g. (0.022 mole) portions of 4-methoxy-2- methyl-6-palmitoylphenol were each shaken at ca. 30 C. with 2 g. of 10% palladium on charcoal catalyst and 250 cc. of glacial acetic acid under hydrogen at 30-40 p. s. i. overnight. The suspensions of product and catalyst were combined and poured into water. The organic material was taken up in ether. The ether layer was filtered, and concentrated under vacuum until most of the acetic acid was distilled off, whereupon the product solidified. The solid was dissolved by warming with 120 cc. of 95 alcohol. On cooling, the solution formed a thick slurry which was diluted with more alcohol to form a workable mixture. Filtration gave 12.3 g. (76%) pure white solid, M. P. 70-7l.5.

2-hexadecyl-6-methylhydroquinone A solution of 9.7 g. (0.027 mole) of 6-hexadecyl-4- methoxy-Z-methylphenol in 500 cc. of glacial acetic acid and 50 cc. of 48% hydrobromic acid was refluxed for 24 hours. The solution was poured into two volumes of water and cooled under tap water for one hour. The precipitate was collected (9.2 g.; M. P. 83-86") and redissolved by refiuxing in a mixture of 280 cc. of petroleum ether (b 35-60") and 530 cc. of ligroin (b 90-120). On standing overnight 6.7 g. of crystals (M. P. 91-92") formed. Recrystallization from 250 cc. of petroleum ether and 350 cc. of ligroin gave 7.1 g. (76%) M. P. 93.5-94.5 C.

The antistain agents of our invention are useful, in general, with emulsions containing couplers incorporated in the manner described in Mannes and Godowsky U. S. Patent 2,304,940 or Jelley and Vittum U. S. Patent 2,322,027.

Couplers such as those described in Weissberger U. S. Patent 2,298,443 and Salminen and Weissberger U. S. Patent 2,423,730, when incorporated in this way, produce dyes upon color development which are prone to fading by the action of visible or ultraviolet light, when known antistain agents such as 2,5-di-tert. octyl hydroquinone are used in the emulsion layer. These are the yellow and cyan dyes. The magenta dyes, such as those formed from couplers described in Loria, Weissberger and Vittum U. S. Patent 2,600,788 are relatively little affected by the known antistain agents upon the action of light.

In order to illustrate the effect of our antistain agents, the following test was made.

A quantity of the antistain agent, the molar equivalent of 0.05 g. of 2,5-di-tert. octyl hydroquinone, was dissolved with 0.5 g. of coupler in 1.5 cc. of dibutylphthalate. To this solution was added 11 cc. of 10% gelatin solution and 2.8 cc. of 5% alkanol B (sodium alkyl naphthalene sulfonate) solution. The resulting mixture was passed through a colloid mill three times, and to the resulting dispersion, 32 cc. of a gelatino-silver halide emulsion were added, and the mixture blended and coated on a film sup- G. Z-amino-S-diethylamino toluene HCl 2 Sodium sulfite (desiccated) 2 Sodium carbonate, monohydrate 20 Potassium bromide 2 Water to 1 liter.

This was followed by 5 min. in the following stop bath:

Sodium sulfite, desiccated g 75 Acetic acid (28%) cc 235 Boric acid, crystals g 27.5 Potassium alum g 75 Water to 1 liter.

After washing, bleaching in ferricyanide-bromide, fixing in 30% hypo solution, and again washing, the wavelength-density curves for each coating were read before and after exposure in the fadeometer for 6 hours. From the resulting curves the losses in density at maximum absorption of the resulting dye, as shown by a plot of density against wave-length, were determined. The following table shows the results:

These results show that all of the antistain agents cause less fading of the cyan and yellow dyes than that caused by 2,5-di-tert. octyl hydroquinone.

The antistain agents of our invention may also be used in non-sensitive overcoating or filter layers, such as a colloidal silver interlayer of multilayer photographic material. In general, the antistain agents of our invention are used in the emulsion or other layer in quantities ranging from 0.07 gram to 4.3 grams per liter of emulsion or gelatin solution. These values are, however, merely illustrative.

In certain cases the antistain agents of our invention may be incorporated in a processing solution such as a prebath, first developer bath, or color-forming developer used with color film which is developed with a primary aromatic amino developing agent.

Our materials are particularly useful with color-forming emulsions coated on paper supports where it is especially important to reduce the minimum or fog densities. This applies both to negative developed paper and to reversal paper as well as to transparency materials.

It will be understood that the examples and modifications described herein are illustrative only and that our invention is to be taken as limited only by the scope of the appended claims.

We claim:

1. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound capable of coupling with the oxidation product of a primary aromatic amino color developer to form a dye and as an antistain agent an unsymmetrical dialkyl hydroquinone having the formula where R represents an alkyl group of from 2 to 18 carbon atoms and R represents a methyl group, R being attached to the hydroquinone nucleus in a position selected from the class consisting of 5 and 6 positions.

2. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound capable of coupling with the oxidation product of a primary aromatic amino color developer to form a dye and as an antistain agent an unsymmetrical 2,5- dialkyl hydroquinone having the formula where R represents an alkyl group of from 2 to 18 carbon atoms.

3. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diifusing coupler compound capable of coupling with the oxidation product of a primary aromatic amino color developer to form a dye and as an antistain agent 2-n-hexadecyl-5-methyl hydroquinone.

4. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound capable of coupling with the oxidation product of a primary aromatic amino color developer to form a dye and as an antistain agent 2-sec. octadecyl-S-methyl hydroquinone.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A COLOR-FORMING PHOTOGRAPHIC EMULSION HAVING REDUCED FOGGING TENDENCY, COMPRISING A SILVER HALIDE EMULSION HAVING INCORPORATED THEREIN A NON-DIFFUSING COUPLER COMPOUND CAPABLE OF COUPLING WITH THE OXIDATION PRODUCT OF A PRIMARY AROMATIC AMINO COLOR DEVELOPER TO FORM A DYE AND AS AN ANTISTAIN AGENT AN UNSYMMETRICAL DIALKYL HYDROQUINONE HAVING THE FORMULA 